1. Field of the Invention
The present invention relates to a control of a hybrid vehicle including an exhaust-gas driven generator, a motor generator, and a battery, in particular, a control device for a hybrid vehicle including an exhaust-gas driven generator and a method of controlling a hybrid vehicle including an exhaust-gas driven generator, which are configured to control the exhaust-gas driven generator and the motor generator while monitoring a power storage state of the battery when an acceleration request is issued.
2. Description of the Related Art
A hybrid vehicle includes a motor generator in addition to an internal combustion engine (hereinafter also referred to simply as “engine”) as a driving source of a vehicle for the purpose of reducing fuel consumption of an automobile. In the hybrid vehicle described above, it is common to use regenerative power of the motor generator, which is generated during deceleration of the vehicle, as power for driving the motor generator. In recent years, however, the regenerative power generated during deceleration is not sufficient as the power for driving the motor generator under the effect of a higher output of the motor generator, which is obtained by increasing a voltage of the motor generator. As a result, there is a problem in that fuel efficiency is lowered due to an operation of the engine for power generation by the motor generator.
The internal combustion engine discards exhaust-gas energy after combustion. Therefore, there is proposed the following hybrid vehicle including an exhaust-gas driven generator (see Japanese Patent Application Laid-open Nos. 2008-274797 and 2009-126303). Specifically, the exhaust-gas energy is recovered as electric energy by the exhaust-gas driven generator driven by a turbine provided in an exhaust-gas passage, and is supplied to the motor generator. In this manner, low fuel consumption can be realized.
Japanese Patent Application Laid-open No. 2008-274797 proposes the following hybrid vehicle. In the hybrid vehicle including the exhaust-gas driven generator, the motor generator is operated by exhaust-gas power generation. Operations of the engine, the motor generator, and the exhaust-gas driven generator are controlled so that fuel consumption for a total output of the engine and the motor generator becomes the smallest during the operation of the motor generator.
Moreover, Japanese Patent Application Laid-open No. 2009-126303 proposes the following hybrid vehicle. In the hybrid vehicle including the exhaust-gas driven generator, the motor generator is driven by power from a battery without the exhaust-gas power generation because of insufficient exhaust-gas energy in an early phase of acceleration of the vehicle. After the vehicle is accelerated to a certain speed and a level of the exhaust-gas energy rises sufficiently, the motor generator is driven by power generated by the exhaust-gas power generation.
However, the related art has the following problems.
In Japanese Patent Application Laid-open No. 2008-274797, the minimization of the fuel consumption is taken into consideration. Therefore, the power is generated by the exhaust-gas power generation even when the vehicle is accelerated. As a result, the output of the engine is disadvantageously lowered. Thus, there is a problem in that an acceleration requested by a driver cannot be obtained. Moreover, a power storage state of the battery is not taken into consideration in the case of the exhaust-gas power generation. Therefore, there is another problem in that the battery cannot be maintained in an optimal charged state.
In Japanese Patent Application Laid-open No. 2009-126303, the power is generated by the exhaust-gas power generation in the early phase of the acceleration of the vehicle in consideration of the presence/absence of the exhaust-gas energy. Therefore, even when the energy of the exhaust gas is obtained, the output is disadvantageously lowered by a pumping loss of the engine due to an increased pressure of the exhaust gas resulting from the exhaust-gas power generation. As a result, there arises a problem in that the acceleration requested by the driver cannot be obtained or a combustion temperature in the engine is increased by the increased pressure of the exhaust gas to cause a trouble such as knocking and pre-ignition in the engine.